Photocatalytic　overall　water　splitting　(OWS)　is　an　appealing　strategy　to　convert　solar　energy　and　produce　hydrogen　fuel.　NiTiO3　(NTO)　is　an　earth-abundant　material,　which　is　studied　as　a　robust　photocatalyst　with　broad　absorptance　of　sunlight　spectrum,　ranging　from　ultraviolet　to　infrared　regions.　Herein,　by　a　rational　design　of　an　NTO-based　photocatalytic　system,　the　activity　for　photocatalytic　OWS　is　realized　under　both　ultraviolet　and　visible　light　illuminations,　and　H2　and　O2　evolution　is　achieved　within　the　stoichiometric　ratio　of　2:1.　Specifically,　Gallium　is　doped　into　the　NTO　crystal　to　activate　the　material　for　photocatalytic　OWS　by　improving　photoexcited　charge　migration.　Meanwhile,　Co　and　Pt　species　are　screened　out　as　the　oxygen　evolution　and　hydrogen　evolution　co-catalysts,　respectively.　Theoretical　stimulations,　steady　state　experiments,　and　operando　characterizations　are　acquired　to　investigate　the　OWS　performance.　This　research　paves　the　pathway　to　apply　this　small-bandgap　photocatalyst　for　OWS　by　maximizing　the　solar　energy　harvesting.　©　2022　Wiley-VCH　GmbH.